This invention relates to a method and apparatus for aligning a plurality of electron beams with the magnetic field of a deflection yoke for producing convergence of the beams on a scanned raster.
The most common type of color television receiver in current use utilizes a delta gun shadow mask picture tube in which three electron beams emanating from the apices of a triangle formed by the guns are deflected to scan a raster on the phosphor screen. It is essential that the electron beams remain converged at all points on the screen so that the three different color rasters are superimposed. To this end it is common practice to utilize an electromagnetic dynamic convergence correction apparatus disposed around the neck of the color picture tube in the region where the beams leave the gun. This convergence correction apparatus usually comprises three electromagnets disposed around three internal pole pieces of the picture tube, which electromagnets are energized at the line and field scanning rates for dynamically controlling the amount of correction imparted to the respective beams to ensure satisfactory convergence at all points on the screen. The waveforms applied to the electromagnets may be suitably adjusted for providing the desired correction. Although this dynamic correction apparatus performs satisfactorily, it is relatively complex and hence relatively expensive, thereby adding to the cost of the color television receiver. Furthermore, the complexity of the apparatus requires considerable time to be adjusted correctly.
Color television picture tubes utilizing three horizontal in-line electron beams have been used in some instances to replace the delta gun picture tubes to simplify the apparatus required to maintain convergence of the beams. For example, in a color television picture tube utilizing three horizontal in-line beams and a phosphor element viewing screen utilizing a pattern of vertical different color phosphor strips, apparatus providing dynamic convergence can be simplified, although dynamic convergence is still required. It is obviously desirable to provide a color television receiver which requires no dynamic convergence correction at all.
Accordingly, it is an object of this invention to provide a method of electron beam and deflection yoke alignment for producing convergence of plural in-line beams.
It is another object of this invention to provide apparatus for electron beam and deflection yoke alignment for producing convergence of plural in-line beams.
In accordance with the invention a method is provided of mounting a beam deflection yoke relative to a color picture tube including an electron gun for projecting a plurality of in-line electron beams toward a phosphor screen, comprising supporting the picture tube in a predetermined position, temporarily supporting the yoke loosely around the picture tube, operating the tube and yoke to project the beams toward the screen and to scan separate rasters thereon and simultaneously adjusting the transverse position of a yoke relative to the picture tube while maintaining substantial parallelism of the longitudinal axis of the yoke and the picture tube to achieve substantial convergence of the beams on the screen, and fixedly attaching the yoke to the picture tube in the adjusted position.
A system for converging a plurality of beams in a color television display system includes a color picture tube including a color phosphor element screen at one end thereof and an electron gun assembly within a neck portion of the tube at the other end thereof for producing a plurality of in-line beams. A deflection yoke adapted to be energized to cause the beams to scan rasters on the phosphor element screen has a smallest inner diameter larger than the outer diameter of the neck portion of the picture tube. Means are provided for allowing the deflection yoke to be adjusted in directions transvere to the central longitudinal axis of the picture tube while maintaining substantial parallelism between the central longitudinal axis of the yoke and the picture tube and for fixedly retaining the yoke in a position providing substantial convergence of the beams on the phosphor element screen.